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Arterial supply to brain:Ophthalmic artery and branches
The ophthalmic artery (OA) is a branch off the C6 segment of the internal carotid artery. It rises medial to the anterior clinoid process as the internal carotid artery emerges from the roof of the cavernous sinus. It originates from the antero- or supero-medial surface of the ICA. Course # The vessel pass through the optic canal in to the orbit, accompanied by the optic nerve superomedially to the artery. # In the orbit, it pierces the dura and spirals around the lateral side of the optic nerve. # It has numerous branches that follow the branches of the nasociliary, frontal and lacrimal nerves. Branches Orbital group (ethmoid air cells, external nose, eyelid, forehead, nasal cavity) ' * ''lacrimal artery: runs superior to superior rectus, to the lacrimal gland, conjunctiva &eyelids. Gives off zygomaticofacial & zygomaticotemporal arteries & a recurrent meningeal branch which anastomoses with middle meningeal artery. * supraorbital artery: passes through supraorbital foramen to supply lateral forehead. * posterior ethmoidal artery: runs inferior to superior oblique through the posterior ethmoidal foramen to supply the middle, posterior ethmoid & sphenoid air cells and anterosuperior nasal cavity. * anterior ethmoidal artery: passes through the anterior ethmoidal foramen upwards into the anterior cranial fossa, then through cribriform plate to supply the anterior nasal cavity and frontal & anterior ethmoid air cells. Gives meningeal branch to anterior cranial fossa. * internal palpebral artery * supratrochlear artery (frontal artery): passes under trochlear (frontal) notch to supply medial forehead. Terminal branch. * dorsal nasal artery: pierces orbicularis oculi & descends to bridge of nose. '''Ocular group (eyes) * central retinal artery: lies inferolateral to CN II, pierces CN II running within it to the optic disc to supply the retina. * long posterior ciliary arteries * short posterior ciliary arteries * anterior ciliary artery: arise from the lacrimal or muscular branches and supply the ciliary body, iris & conjunctiva. * posterior ciliary - pierce the sclera to enter the choroid coat of the eye. * muscular artery Variant anatomy Embryologically, the orbit has dual supply from the supraorbital branch (which later becomes the middle meningeal artery) and from the OA but there can be often be variation: * communicating branch between the ophthalmic and middle meningeal artery is present; most frequently passes through the superior orbital fissure (up to 50%) * when multiple branches are present (15%) then an additional small foramen (or multiple foramen) lateral to the superior orbital fissure are present (foramen of Hyrtl or the meningo-orbital foramen) ** the connecting branch is known as sphenoidald artery or recurrent meningeal artery or orbital branch of the middle meningeal branch * regression of proximal ophthalmic artery and entire orbit is supplied by the middle meningeal artery. These variants are important to recognise as embolisation of a tumour supplied by the external carotid artery (e.g. meningioma or haemangiopericytoma) can result in blindness. This is reported as the most common variant origin and in this case OA enters the orbit via the superior orbital fissure or via its own canal. Variations in origin or branching patterns may be common: * middle meningeal can arise from the ophthalmic artery. * ophthalmic artery origin from the middle meningeal artery * cavernous origin of ophthalmic artery is less common